Minor clean-up

* Some big fixes in enslib: default for `save_path` argument in
  `plot_spot_ensemble` now `None` rather than `'None'` (can't believe I
  did that...); wind_speed data copied before cobversion to leave
  original units intact.
* In `saildocs`: force *model* to lower case in `parse_spot_request` so
  request with 'send SPOT:GFS:' and 'send SPOT:GEFS:' will be handled
  correctly.
* In `windbreaker.process_query` replaced hard-coded `'ens'` with
  `conv.ENSEMBLE`